1. Field
Example embodiments relate to a storage node including a diffusion barrier layer, a phase change memory device having the same and methods of manufacturing the same. Other example embodiments to storage node that suppresses titanium (Ti) diffusion and a method of manufacturing the phase change memory device.
2. Description of the Related Art
In general, phase change memory devices (e.g., phase change random access memories) include a storage node with a phase change layer and a transistor connected to the storage node. The phase change layer changes from a crystalline state to an amorphous state, or vise versa, according to the voltage applied thereto. If the applied voltage is a set voltage, the phase change layer changes from the amorphous state to the crystalline state. If the applied voltage is a reset voltage, the phase change layer changes from the crystalline state to the amorphous state.
One of the crystalline state and the amorphous state of the phase change layer corresponds to data 1 while the other corresponds to data 0. The resistance of the phase change layer, if the phase change layer is in the crystalline state, may be smaller than that the resistance of the phase change layer in the amorphous state. The current measured when the phase change layer is in the crystalline state is larger than that when the phase change layer is in the amorphous state.
Data recorded on the phase change layer may be read by comparing the current measured by applying a read voltage to the phase change layer with a reference current.
The conventional phase change memory devices include a storage node having a phase change layer, (e.g., a germanium-antimony-tellurium (GeSbTe) layer commonly referred to as “GST” layer). A titanium (Ti) layer and a titanium nitride (TiN) layer may be sequentially deposited (or formed) on the phase change layer. The TiN layer is used as a top electrode contact layer. The Ti layer is used as an adhesion layer to increase the adhesive force of the TiN layer.
As a write operation or a read operation is repeated in the conventional memory device, Ti diffuses from the Ti layer to the phase change layer. As such, the composition and resistance of the phase change layer may change such that defects are generated in the conventional memory devices. For example, a set stuck failure and a reset stuck failure may occur as a result of the diffusion of Ti during an endurance test of the conventional memory device.
It may be seen from FIGS. 1 through 3 that Ti diffuses to a phase change layer of a storage node of a conventional memory device.
FIG. 1 illustrates a transmission electron microscopy (TEM) image of the storage node of the conventional phase change memory device after an annealing process at 350° C. for 1 hour.
Referring to FIG. 1, a bottom electrode 2 may be a TiN electrode, a phase change layer 4 may be a GST layer, an adhesion layer 6 may be a Ti layer and a top electrode 8 may be a TiN electrode.
FIG. 2 illustrates a high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the annealed storage node of FIG. 1. FIG. 3 is an energy dispersive spectroscopy (EDS) data displaying element profiles along line a-a′ of FIG. 2.
Referring to FIG. 3, Ti diffuses into the GST layer (i.e., the phase change layer). Te having a higher affinity for Ti moves (or migrates) to the adhesion layer 6.
Sb and Ge move (or migrate) in a direction opposite to that of the Te (i.e., away from the adhesion layer). If the Ti diffuses to the phase change layer, the composition of the phase change layer may change.